The molecular mechanisms by which troponin and tropomyosin regulate the interaction of actin and myosin in skeletal and cardiac muscle will be investigated, involving a detailed study of the changes in structure and interactions among the troponin subunits and the other thin filament proteins, actin and tropomyosin. This will be approached by studying a) the effect of metals on the structure of TnC and its complexes with the other troponin subunits and with tropomyosin and actin; b) the effect of chemical modification of specific amino acid residues in these proteins to identify functionally important regions; and c) peptide fragments produced by chemical or enzymatic cleavage at specific sites in the sequence.